Various types of transmission devices have been developed that transmits rotation of a drive shaft to a driven shaft that has an axis extending along a direction different from the axis of the drive shaft. Such a transmission device transmits rotation by meshing a worm gear attached to a drive shaft and a helical gear attached to a driven shaft, and includes a support member to rotatably accommodate the worm gear and the helical gear.
Patent Document 1 discloses a transmission device that includes four bearing portions each supports one of the ends of a worm gear and the ends of a helical gear. The bearing portions are formed by dividing a support member into four pieces.
However, in the transmission device disclosed in Patent Document 1, the positional accuracy of the bearing portions, or the positional accuracy of each of the parts obtained by dividing the support member into four pieces, affects the meshing of the worm gear and the helical gear. That is, if the positional accuracy of the parts is reduced when assembling the four bearing portions, noise may be generated between the meshing worm gear and helical gear. It is therefore necessary to ensure the positional accuracy of the bearing portions.
Patent Document 2 discloses a gear housing serving as a support member that integrally includes four bearing portions each supporting one of the ends of worm gear and the ends of the helical gear. However, since the gear housing is shaped like a box, the drive shaft and the drive shaft each need to be moved along the axial direction when being assembled. This makes the assembly of the worm gear and the helical gear burdensome.
[Patent Document 1] Pamphlet of International Patent Publication 2005/015054 A1
[Patent Document 2] Japanese Laid-Open Patent Publication No. 2000-16127